Tag Archives: quantum physics

Measuring a superconducting qubit by manipulating its environment

Matthew Francis of ArsTechnica talks about the difficulty of measuring quantum states with disturbing it, and a new method that has been developed to work around that difficulty:

A new paper describes how to use environmental measurements to gain information about a quantum system that would otherwise be unavailable. K. W. Murch, S. J. Weber, C. Macklin, and I. Siddiqi controlled a superconducting quantum system called a transmon by performing measurements on the cavity in which it resided. In that way, they were able to monitor the transition between quantum states in the transmon without directly interacting with it. This experiment demonstrates an effective way to get around decoherence in at least some systems, which could be significant for quantum computing.

You can read the original paper over at Nature.

The Quantum Atom

Quantum physics: The quantum atom

Following the 100th birthday of Niels Bohr’s atom, a special issue of Nature celebrates and explores the origin and legacy of Bohr’s quantum atom.

Bohr’s model: Extreme atoms

A look into how particle physicists are pushing the limits of what an atom can become, by remove electron or overloading the nucleus with protons and neutrons.

History: The path to the quantum atom

John L. Heilbron takes a walk back into history and looks at the path which led Niels Bohr to quantize electron orbits a century ago.

Physics: The enigmatic electron

Frank Wilczek talks about the complex implications behind the simple properties of the electron and how we are still investigating its true nature.

Looking at frustrated magnetism

In a paper by R. Islam et al from the Joint Quantum Institute and the Dept. of Physics at Harvard, researchers take a look at one of the factors in emergent complexity of many-body systems – competition between interacting components in a network, or also aptly termed as frustration.

This leads to frustrated magnetism in complex systems such as quantum spin liquids, spin glasses and spin ices, which can carry high degrees of quantum entanglement and be massively degenerate.

By creating frustrated antiferromagnetic interactions by spins stored in a crystal of up to 16 trapped Ytterbium atoms, they look to control the amount of frustration by continuously tuning the range of interaction and measuring the spin dynamics.

Read more about this in their Science research paper: Emergence and Frustration of Magnetism with Variable-Range Interactions in a Quantum Simulator

Viewing the Uncertainty Principle on a macro scale

Slit_uncertainty_principle-300x197

In 1927, Werner Heisenberg developed his famous Uncertainty Principle which stated that you could not precisely measure both an object’s position and momentum at the same time.

His classic example was using a photon to measure an electron – when the photon bounced off the electron, it would have changed the momentum and position of the electron. You could either measure either variable but not both.

This issue generally doesn’t apply to macroscopic objects but physicist Tom Purdy and his team at JILA in Boulder, Colorado, wanted to show it at the macro scale so they built a device to measure the quantum back-action effect in the optical measurement of a mirror, which involved measuring the vibration of the mirrors from the photons hitting them.

Read Gerard’s perspective on this experiment at Science

Read Tom Purdy’s full article at Science.

Short Book Reviews

Peter Woit has written a series of short reviews on quantum physics books here: http://www.math.columbia.edu/~woit/wordpress/?p=5487

 If you’re interested to borrow the reviewed books, you can find them at Lee Wee Nam Library

The Theoretical Minimum (on order)

Lectures on Quantum Mechanics (on order)

The Conceptual Framework of Quantum Field Theory

Advanced Topics in Quantum Field Theory

ABC of Physics: A very brief guide